powerpc/ps3: Fix lv1 hcall assembly for ELFv2 calling convention

Stack-passed parameters begin at a different offset in the caller's
stack in the ELFv2 ABI.

Reported-by: Geoff Levand <geoff@infradead.org>
Fixes: 8c5fa3b5

 ("powerpc/64: Make ELFv2 the default for big-endian builds")
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Tested-by: Geoff Levand <geoff@infradead.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20231227072405.63751-2-npiggin@gmail.com